1. Field of the Invention
The present invention relates in general to a fluid-filled vibration damping device having fluid chambers filled with a non-compressible fluid and constructed to provide a vibration damping effect based on flows of the fluid between the fluid chambers. More particularly, the present invention is concerned with such a fluid-filled vibration damping device having a primary fluid chamber to which a vibrational load is applied, and an auxiliary fluid chamber whose volume is variable, and wherein a partition structure which separates the primary and auxiliary fluid chambers from each other includes a movable rubber plate which is elastically deformable so as to permit or control the fluid flows.
2. Discussion of the Related Art
There is known a fluid-filled vibration damping device such as an engine mount and a body mount for an automotive vehicle. As disclosed in JP-U-4-101833 and JP-A-4-357344, such a fluid-filled vibration damping device includes a first mounting member and a second mounting member which are spaced apart from each other and which are elastically connected to each other by an elastic body that partially defines a primary fluid chamber filled with a non-compressible fluid. The damping device further includes a partition structure supported by the second mounting member, and a flexible diaphragm which partially defines an auxiliary fluid chamber also filled with the non-compressible fluid. The primary and auxiliary fluid chambers are located on the opposite sides of the partition structure, respectively, and communicate with each other through an orifice passage formed through the partition structure. The vibration damping device further includes a movable rubber plate which is supported at its peripheral portion by the partition structure and which also partially defines the primary fluid chamber.
In such a known fluid-filled vibration damping device as described above, the partition structure separating the primary and auxiliary fluid chambers from each other is generally advantageously constituted by a combination of a plurality of components which are fixedly superposed on each other in the axial direction of the damping device in which the first and second mounting members are spaced apart from each other. This arrangement of the partition structure permits comparatively easy formation of the orifice passage having a sufficient length, resulting in an increased degree of freedom in tuning the vibration damping characteristics of the vibration damping device. The same arrangement also permits easy formation of a gas-tightly enclosed air chamber on one side of the movable rubber plate remote from the primary fluid chamber. The provision of the air chamber facilitates the adjustment of the spring characteristics of the movable rubber plate, and makes it possible to easily control the vibration damping characteristics of the device by periodically changing the pressure in the air chamber so as to oscillate the movable rubber plate.
Where the partition structure consists of two or more components superposed on each other as described above, it is important to construct the partition structure so as to assure a sufficient degree of fluid-tight sealing at the interfaces of the components, for preventing leakage flows of the fluid from the primary and auxiliary fluid chambers and the orifice passage and for securing high gas tightness of the air chamber, in order to permit the damping device to exhibit the desired vibration damping characteristics with high stability.
In view of the sealing requirement indicated above, it has been proposed to form all of the components of the partition structure of a thermoplastic synthetic resin and fusion-weld these resin components together after they are superposed on each other. Alternatively, the components are superposed on each other in the axial direction of the damping device such that the movable rubber plate is gripped at its peripheral portion by the adjacent components, and such that the components are pressed against each other by the second mounting member.
However, the partition structure consisting of the mutually fusion-welded synthetic resin components is comparatively difficult to manufacture and is accordingly expensive. This partition structure has another drawback, that is, difficulty to assure a sufficiently high degree of reliability of sealing at the interfaces of the components.
In the partition structure wherein the superposed components are pressed against each other so as to grip the peripheral portion of the movable rubber plate, the pressing force directly acts on the peripheral portion of the movable rubber plate, causing an adverse effect on the spring characteristics of the movable rubber plate, or a variation in the spring characteristics, resulting in deterioration of the vibration damping characteristics of the damping device and reduction in the durability of the movable rubber plate. Further, the components of the partition structure of this type are subject to bending stresses due to the pressing force applied by the second mounting member, and are required to have comparatively large wall thickness and high rigidity in order to assure sufficient mechanical strength and deformation resistance and sufficient durability.